# OCR Gateway Science B Additional Higher P4- Safe Electricals

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• Created by: parrot16
• Created on: 07-04-15 15:30

What is an electric current?

The rate of flow of electric charge measured using an ammeter in amps.

What is charge carried by in a circuit?

Negatively charged electrons which flow in the opposite direction to conventional current

Conventional current

Electric charge flows from the positive terminal to the negative terminal because electrons are negative and the same charges repel.

What do resistors do?

Limit the amount of current that flows in a circuit

What wires have more resistance?

Long and thin wires

What wires have less resistance?

Short and think wires

What is resistance measured in?

Ohms

Why do longer wires have more resistance?

The resistance of a wire changes if its length changes. This makes sense if you consider that there are a number of collisions between the electrons and the ions when electricity flows through 1 metre of a wire. There are twice as many collisions when electricity flows through 2 metres and 3 times as many collisions when electricity flows through 3 metres etc.

What happens as resistance increases?

Current decreases

What is a rheostat/variable resistor and what does it do?

Used to control current flow in the circuit by changing the resistance. The slider alters the length of the wire in the circuit

Another word for voltage?

Potential difference

What happens as voltage increases?

Current increases

What is ohms law

The current flowing through a wire is proportional to the potential difference across it provided that the temperature is the same

What happens in a fixed resistor as the voltage increases?

The current increases

What happens in a fixed voltage as the resistance increases?

The current decreases

What is resistance?

Measurement of how hard it is for an electric current to flow

What is current?

Flow of electrons

What is voltage?

A measurement of energy carried by an electrical current

What color is the fuse?

Red

What color is the earth wire?

Yellow or green

What color is the neutral wire?

Blue

What color is the live wire?

Brown

What does the live and neutral wire do?

Connect a house to a power station

What does the live wire do?

Carries high voltage into and around the house

What does the neutral wire do?

Completes the circuit by providing a return path for the current to an electricity substation to be earthed

What does the earth wire do?

It is a safety wire and is connected to metal casings of the appliance to prevent it becoming live if the live wire comes into contact with it

When can a fault occur?

When live and neutral wires touch or when the live wire touches the casings of the…

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